37 processes sounds within the norm. Mine is XP home, and it's running 36.
201,202K is an excessive amount, virtually all of your memory; the process name is important, as it indicates a problem with that process.
There are two types of memory; the capacity of your disk (hard drive) to store what you want or need to put on it, such as files, photos, operating system etc, and the RAM, which basically runs active processes..programs that are running. How full the disk is (until it's near max) will have virtually no impact on how fast the computer works. So deleting files won't make a difference, there.
You have enough RAM; what you need to find out is what is using it all. It is likely to be something that runs at startup, and, with the amount of usage you're mentioning, it's fairly likely to be a malicious process.
So, restart the computer, look in taskmanager again, find the process that you originally stopped that is using the most RAM, (not a good or permanent fix, by the way) and report the name of it, please.